Grammar is essential when studying a language.
However grammar is hard to learn, isn't it?
There are many people who think that if we can speak, we don't have to learn grammar.
Then, why do we need to study grammar?
That's to be expressive.
Every sentence said, "I ate sushi."
However, don't you think that the sentence (3) better than the sentence (1)
will tell you what kind of sushi I ate and how I felt?
I think it's necessary for you and me to study grammar and be able to use grammar to enrich our expressions.